Paper typically includes binders and/or coatings to improve its optical and printing properties. For example, synthetic latexes can be used as components of pigmented coatings to increase the strength and the printability of the paper. For pigmented paper coating formulations, the solids content can influence the runnability of the coatings in the paper coating machine by affecting the viscosity of the coatings and their flow behavior at varying stresses in the coating machine. High solids content may be desired to save drying energy and to improve coating holdout for better printing quality. High water retention capacity may also be desired so as to prevent significant dewatering between the application and metering process steps.
When a paper coating formulation having a synthetic latex is subjected to high shear, such as, for example, in a blade coater, the formulation can exhibit a shear thinning or shear thickening behavior. Decreasing the solids content in the coating formulation may reduce shear thickening thereby improving the runnability of the formulation, but the quality of the resulting coating can be adversely affected by lower solids content and may also lead to excess absorption of water into the paper substrate, resulting in higher instances of web breaks.
Paper coating formulations that can be run at increasingly higher solids content can facilitate the production of high quality paper, increase production rates, and reduce energy costs. Conventional synthetic latexes may be limited in their use as paper coatings with high solids content due to the resulting high viscosity of the coating formulations at high shear rates.